i have an iphone 3g that was accidentally upgraded to 3.1.3, prior to the upgrade my phone was unlocked for my tmobile sim card, but since the upgrade i am not able to use my sim...I have tried to downgrade back to the 3.1.2 in order to unlock the phone again and start fresh but i havent been able to!! HELPPPPP!! i was also wondering if i were to use someone else's att sim would i be able to downgrade back to the 3.1.2 then unlock since unlocking a 3.1.3 is apparently not able to happen. plzzzzz help, open to any suggestions!